Most biological assay systems rely on expensive instrumentation for analysis. Very often, this analysis involves detecting changes in optical properties, such as absorbance or fluorescence, within reaction volumes over time. These optical property signals are then analyzed and a determination is made about an analyte within a biological sample often for health monitoring or disease diagnosis. As healthcare costs increase, there is substantial interest in developing low-cost diagnostic devices that can be used outside of traditional laboratory settings, e.g. point-of-care clinics, pharmacies, or in the home. Furthermore, many biological assays chemistries have become available that simplify sample preparation workflows (e.g. eliminating purification requirements) and result analysis (e.g. by relying on colorimetric analysis), making them ideal for these settings. However, a key challenge remains in the design of low-cost instrumentation to enable accurate measurement of optical changes in reaction volumes while simultaneously regulating reaction temperature.